# Move all zeros to start and ones to end in an Array of random integers

• Difficulty Level : Easy
• Last Updated : 23 May, 2022

Given an array arr[] of random integers, the task is to push all the zero’s in the array to the start and all the one’s to the end of the array. Note that the order of all the other elements should be the same.
Example:

Input: arr[] = {1, 2, 0, 4, 3, 0, 5, 0}
Output: 0 0 0 2 4 3 5 1
Input: arr[] = {1, 2, 0, 0, 0, 3, 6};
Output: 0 0 0 2 3 6 1

Approach: Traverse the array from left to right and move all the elements which are not equal to 1 at the beginning and then put 1’s in the rest of the indices at the end of the array. Now, find the index of the last element which is not equal to 1 say lastInd and then starting from this index to the beginning of the array push all the elements which are not equal to 0 in the end till lastInd and then put 0’s in the beginning.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Utility function to print``// the contents of an array``void` `printArr(``int` `arr[], ``int` `n)``{``    ``for` `(``int` `i = 0; i < n; i++)``        ``cout << arr[i] << ``" "``;``}` `// Function that pushes all the zeros``// to the start and ones to the end of an array``void` `pushBinaryToBorder(``int` `arr[], ``int` `n)``{` `    ``// To store the count of elements``    ``// which are not equal to 1``    ``int` `count1 = 0;` `    ``// Traverse the array and calculate``    ``// count of elements which are not 1``    ``for` `(``int` `i = 0; i < n; i++)``        ``if` `(arr[i] != 1)``            ``arr[count1++] = arr[i];` `    ``// Now all non-ones elements have been shifted to``    ``// front and 'count1' is set as index of first 1.``    ``// Make all elements 1 from count to end.``    ``while` `(count1 < n)``        ``arr[count1++] = 1;` `    ``// Initialize lastNonBinary position to zero``    ``int` `lastNonOne = 0;` `    ``// Traverse the array and pull non-zero``    ``// elements to the required indices``    ``for` `(``int` `i = n - 1; i >= 0; i--) {` `        ``// Ignore the 1's``        ``if` `(arr[i] == 1)``            ``continue``;``        ``if` `(!lastNonOne) {` `            ``// Mark the position Of``            ``// last NonBinary integer``            ``lastNonOne = i;``        ``}` `        ``// Place non-zero element to``        ``// their required indices``        ``if` `(arr[i] != 0)``            ``arr[lastNonOne--] = arr[i];``    ``}` `    ``// Put zeros to start of array``    ``while` `(lastNonOne >= 0)``        ``arr[lastNonOne--] = 0;``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 1, 2, 0, 0, 0, 3, 6 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);``    ``pushBinaryToBorder(arr, n);``    ``printArr(arr, n);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``import` `java.util.*;` `class` `GFG``{` `// Utility function to print``// the contents of an array``static` `void` `printArr(``int` `arr[], ``int` `n)``{``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``System.out.print(arr[i]+``" "``);``}` `// Function that pushes all the zeros``// to the start and ones to the end of an array``static` `void` `pushBinaryToBorder(``int` `arr[], ``int` `n)``{` `    ``// To store the count of elements``    ``// which are not equal to 1``    ``int` `count1 = ``0``;` `    ``// Traverse the array and calculate``    ``// count of elements which are not 1``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``if` `(arr[i] != ``1``)``            ``arr[count1++] = arr[i];` `    ``// Now all non-ones elements have been shifted to``    ``// front and 'count1' is set as index of first 1.``    ``// Make all elements 1 from count to end.``    ``while` `(count1 < n)``        ``arr[count1++] = ``1``;` `    ``// Initialize lastNonBinary position to zero``    ``int` `lastNonOne = ``0``;` `    ``// Traverse the array and pull non-zero``    ``// elements to the required indices``    ``for` `(``int` `i = n - ``1``; i >= ``0``; i--)``    ``{` `        ``// Ignore the 1's``        ``if` `(arr[i] == ``1``)``            ``continue``;``        ``if` `(lastNonOne == ``0``)``        ``{` `            ``// Mark the position Of``            ``// last NonBinary integer``            ``lastNonOne = i;``        ``}` `        ``// Place non-zero element to``        ``// their required indices``        ``if` `(arr[i] != ``0``)``            ``arr[lastNonOne--] = arr[i];``    ``}` `    ``// Put zeros to start of array``    ``while` `(lastNonOne >= ``0``)``        ``arr[lastNonOne--] = ``0``;``}` `// Driver code``public` `static` `void` `main(String args[])``{``    ``int` `arr[] = { ``1``, ``2``, ``0``, ``0``, ``0``, ``3``, ``6` `};``    ``int` `n = arr.length;``    ``pushBinaryToBorder(arr, n);``    ``printArr(arr, n);` `}``}` `// This code is contributed by SURENDRA_GANGWAR.`

## Python3

 `# Python3 implementation of the approach` `# Utility function to print``# the contents of an array``def` `printArr(arr, n) :` `    ``for` `i ``in` `range``(n) :``        ``print``(arr[i],end``=``" "``)`  `# Function that pushes all the zeros``# to the start and ones to the end of an array``def` `pushBinaryToBorder(arr, n) :` `    ``# To store the count of elements``    ``# which are not equal to 1``    ``count1 ``=` `0``    ` `    ``# Traverse the array and calculate``    ``# count of elements which are not 1``    ``for` `i ``in` `range``(n) :``        ``if` `(arr[i] !``=` `1``) :``            ``arr[count1] ``=` `arr[i]``            ``count1 ``+``=` `1` `    ``# Now all non-ones elements have been shifted to``    ``# front and 'count1' is set as index of first 1.``    ``# Make all elements 1 from count to end.``    ``while` `(count1 < n) :``        ``arr[count1] ``=` `1``        ``count1 ``+``=` `1` `    ``# Initialize lastNonBinary position to zero``    ``lastNonOne ``=` `0` `    ``# Traverse the array and pull non-zero``    ``# elements to the required indices``    ``for` `i ``in` `range``(n ``-` `1``, ``-``1``, ``-``1``) :` `        ``# Ignore the 1's``        ``if` `(arr[i] ``=``=` `1``) :``            ``continue``            ` `        ``if` `(``not` `lastNonOne) :` `            ``# Mark the position Of``            ``# last NonBinary integer``            ``lastNonOne ``=` `i` `        ``# Place non-zero element to``        ``# their required indices``        ``if` `(arr[i] !``=` `0``) :``            ``arr[lastNonOne] ``=` `arr[i]``            ``lastNonOne ``-``=` `1` `    ``# Put zeros to start of array``    ``while` `(lastNonOne >``=` `0``) :``        ``arr[lastNonOne] ``=` `0``        ``lastNonOne ``-``=` `1` `# Driver code``if` `__name__ ``=``=` `"__main__"` `:``    ` `    ``arr ``=` `[ ``1``, ``2``, ``0``, ``0``, ``0``, ``3``, ``6` `];``    ``n ``=` `len``(arr);``    ``pushBinaryToBorder(arr, n)``    ``printArr(arr, n)` `# This code is contributed by Ryuga`

## C#

 `// C# implementation of the approach``using` `System;` `class` `GFG``{` `// Utility function to print``// the contents of an array``static` `void` `printArr(``int` `[]arr, ``int` `n)``{``    ``for` `(``int` `i = 0; i < n; i++)``        ``Console.Write(arr[i] + ``" "``);``}` `// Function that pushes all the zeros``// to the start and ones to the end of an array``static` `void` `pushBinaryToBorder(``int` `[] arr, ``int` `n)``{` `    ``// To store the count of elements``    ``// which are not equal to 1``    ``int` `count1 = 0;` `    ``// Traverse the array and calculate``    ``// count of elements which are not 1``    ``for` `(``int` `i = 0; i < n; i++)``        ``if` `(arr[i] != 1)``            ``arr[count1++] = arr[i];` `    ``// Now all non-ones elements have been shifted to``    ``// front and 'count1' is set as index of first 1.``    ``// Make all elements 1 from count to end.``    ``while` `(count1 < n)``        ``arr[count1++] = 1;` `    ``// Initialize lastNonBinary position to zero``    ``int` `lastNonOne = 0;` `    ``// Traverse the array and pull non-zero``    ``// elements to the required indices``    ``for` `(``int` `i = n - 1; i >= 0; i--)``    ``{` `        ``// Ignore the 1's``        ``if` `(arr[i] == 1)``            ``continue``;``        ``if` `(lastNonOne == 0)``        ``{` `            ``// Mark the position Of``            ``// last NonBinary integer``            ``lastNonOne = i;``        ``}` `        ``// Place non-zero element to``        ``// their required indices``        ``if` `(arr[i] != 0)``            ``arr[lastNonOne--] = arr[i];``    ``}` `    ``// Put zeros to start of array``    ``while` `(lastNonOne >= 0)``        ``arr[lastNonOne--] = 0;``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `[]arr = { 1, 2, 0, 0, 0, 3, 6 };``    ``int` `n = arr.Length;``    ``pushBinaryToBorder(arr, n);``    ``printArr(arr, n);``}``}` `// This code is contributed by Mohit kumar 29.`

## Javascript

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Output:

`0 0 0 2 3 6 1`

Time Complexity: O(N), where N represents the size of the given array.

Auxiliary Space: O(1), no extra space is required, so it is a constant.

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